1. Field
The inventive concept relates to a method and apparatus for motion estimation (ME) of a video in a video system.
2. Description of the Related Art
In a video system, motion estimation (ME) is performed between respective input frames to compress data or to convert a frame rate. In the video system, a widely used method of performing ME on a temporal axis of the video divides a target video into pixels or pixel blocks, locates a portion most similar to each pixel or pixel block in a previous and a subsequent frame of a temporal order, and calculates a change of a coordinate value. The method will be described with reference to an example shown in FIGS. 1A, 1B and 1C
FIGS. 1A, 1B and 1C are a view illustrating an example of a motion estimation (ME) method in a known video system.
Referring to FIG. 1B, in a known ME method, an image is divided into grids and a portion similar to each divided frame is located in a previous frame ft−1 (FIG. 1A), in a current frame ft (FIG. 1B) and a subsequent frame ft+1 (FIG. 1C). Specifically, in order to estimate temporal motion of a block shown in a bold line in a frame ft in FIG. 1B, a similar block is located in the frame ft−1 (FIG. 1A) and the frame ft+1 (FIG. 1C) by using a cost function such as a mean square error (MSE) and a sum of absolute difference (SAD). A change of a coordinate value between these blocks is calculated to obtain a quantitative motion vector (MV) of the target block.
The conventional ME method as shown in FIGS. 1A, 1B and 1C have a satisfactory accuracy of estimation in case of a video composed of an ordinary natural object. However, in case of a peculiar video as shown in FIG. 2, the accuracy of the motion estimation is not reliable.
FIG. 2 is a view illustrating an example of an image which includes an area having a periodic characteristic (pattern).
When an area in which the same pattern is repeated exists within the video as shown in FIG. 2, respective divided blocks of a corresponding area are very similar to one another, such that an accurate matching block is difficult to locate by using the cost function. This will be described with reference to FIG. 3s. 3A, 3B and 3C.
FIG. 3s. 3A, 3B and 3C are views illustrating a known ME method performed on the image of FIG. 2.
Referring to FIGS. 3A, 3B and 3C, it may not be easy to locate which block in a frame ft−1 (FIG. 3A) or a frame ft+1 (FIG. 3C) corresponds to a block shown in a bold line in a frame ft (FIG. 3B) simply by comparing divided blocks of the video in order to verify the matching block.
As described above, in the known ME method, an ME result may not be accurate depending on the video, which results in a negative effect being generated in a subsequent video processing process using such an intermediate result. As a result, a negative effect is generated in a final result of an entire video processing. For example, in case of a video codec, a size of a compressed video may be increased, or a video quality may deteriorate if the amount of data of the compressed video is limited. In case of a frame rate up conversion (FRUC), the resulting video quality may be deteriorated as a result of erroneous motion estimation.
In order to prevent deterioration of the video quality in the conventional ME method, an assumption is made that an area detected as having a periodic pattern does not have a motion (a zero motion vector is assigned to attempt a local fall-back) or an ME result of the area detected as having the periodic pattern with an overall motion (global motion vector) of a screen may be replaced. However, these conventional ME methods cannot sufficiently compensate for inaccuracy of the ME result and, as a result, cannot solve the problems of deterioration of the video quality or of an increase in the size of the compressed video.